Recurring Priest (Legacy)

Combo is Priest of Gix and Recurring Nightmare
For turn 2 win only need combo and Altar of the Brood and 2 lands a swamp and (Ancient Tomb or City of Traitors).
Turn 1 swamp + Altar of the Brood
Turn 2 (AT or CoT) and cast Priest of Gix enters the battlefield you get 3 black mana, use that mana to cast Recurring Nightmare then use Recurring Nightmare to sacrifice Priest of Gix to return Recurring Nightmare to your hand, and that allows you to return the Priest of Gix to play and get 3 black mana..... then just repeat tell opponent is milled out.

Otherwise turn 3 same idea, except you play either Corpse Knight or Cruel Celebrant on turn 2 and the go off turn 3.

You can add Carnival of Souls in and create infinite black mana on turn 3 and cast Torment of Hailfire as well. That combo looks like this.
Turn 1 either life dork (Soul Warden or Deathgreeter)
Turn 2 Carnival of Souls
Turn 3 Recurring Priest Combo
Then as you use the combo Carnival of Souls triggers you lose life and get 1 black mana, then either life dork triggers and you gain 1 life either on enter of Priest of Gix or on activing Recurring Nightmare. Thus negating Carnival of Souls life loss.

Other addons are Dash Hopes just to prevent anything crazy on your opponents side. Works best in mid to late game after turn 4-5 and you have been playing creatures that drain life from your opponent.
Street Wraith just to help draw cards if you need a piece of the combo. And Genesis Chamber give you a huge army of tokens. You can replace these 3 card sets with anything else that you feel would be better in main deck. Last unique card is Westvale Abbey it's just a big hitter in late games, works well with Genesis Chamber

!!!!!!THIS IS A COMBO DECK!!!!!!!
So it only wins with these effects. However I have space in sideboard to fill with some big creatures that are not the same that you could cycle into the deck incase of Surgical Extraction or Leyline of the Void style cards.

Clear cycles so doesn't stay a dead card, Grand Abolisher makes it so your opponents cant cast spells during your combo, and Pact of Negation and this is only if you know they have a disruption for your combo. Only bring out in game 3 after you know what hate they are running. Only use if you can win the game that turn, otherwise you loss.